Electrocatalysis with dual functionality – an overview
With in situ methods at synchrotron sources complex organic oxidation reactions at catalysts can be analysed in real time. © Debabrata Bagchi / HZB
Schematic illustration of a hybrid electrolyser, which combines hydrogen production at the cathode with the production of valuable organic compounds at the anode by organic oxidation reactions. © Debabrata Bagchi / HZB
In situ and operando techniques allow real-time monitoring of catalyst behaviour under operating conditions. In situ methods also enable observation of adsorption and intercalation of intermediates into catalyst lattices, as well as bond formation and cleavage on the catalyst surface. Furthermore, product selectivity can also be mapped in operando conditions. Active metals used in OOR include Ni, Co, Cu, Mn, Ru, Pt, Pd and Au. © Debabrata Bagchi / HZB
Hybrid electrocatalysts can produce green hydrogen, for example, and valuable organic compounds simultaneously. This promises economically viable applications. However, the complex catalytic reactions involved in producing organic compounds are not yet fully understood. Modern X-ray methods at synchrotron sources such as BESSY II, enable catalyst materials and the reactions occurring on their surfaces to be analysed in real time, in situ and under real operating conditions. This provides insights that can be used for targeted optimisation. A team has now published an overview of the current state of knowledge in Nature Reviews Chemistry.
Hybrid water electrolysers are recent devices, which produce hydrogen or other reduction products at the cathode, while valuable organic oxidation products are formed at the anode. This innovative approach significantly increases the profitability of hydrogen production. Another advantage is that organic oxidation reactions (OOR) for producing the valuable compounds are quite environmentally friendly compared to the conventional synthesis processes which often require aggressive reagents. However, organic oxidation reactions are very complex, involving multiple catalyst oxidation states, phase transitions, intermediate products, the formation and dissolution of bonds, and varying product selectivity. Research on OOR research is still in its infancy.
Review on the state of the art
In Nature Reviews Chemistry, a team of experts led by Dr Prashanth Menezes (HZB) and Prof. Matthias Driess (Technical University of Berlin) provides a comprehensive overview of this exciting field of research. They explain advanced methods and techniques available at synchrotron sources such as BESSY II, where complex reactions can be analysed in real time and in situ.
The overview comprises various catalytic reactions, including the oxygenation of alcohols and aldehydes, the dehydrogenation of amines, the degradation of urea and coupling reactions. The authors present the most useful methods for gaining insight into the complex reaction mechanisms, such as X-ray absorption, Raman and infrared spectroscopy, and differential electrochemical mass spectrometry. In situ methods reveal structural changes in the catalyst, while operando techniques monitor both the structure and activity under real operating conditions. These methods can be used to explore all kinds of catalytic or chemical reaction systems to gain insights into the behaviour of catalysts and reactions under operating conditions. The review contains also a chapter on machine learning methods to evaluate large data sets.
‘This review aims to raise awareness of this exciting research field and encourage scientists to combine different analysis techniques. This will foster the understanding of heterogeneous catalytic reactions and accelerate the development of efficient hybrid electrocatalysts as a sustainable green chemistry technology,’ says Menezes.
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